Ets-2 and Components of Mammalian SWI/SNF Form a Repressor Complex That Negatively Regulates the BRCA1Promoter

Abstract

Ets-2 is a transcriptional activator that can be modulated by ras-dependent phosphorylation. Evidence is presented indicating that ets-2 can also act as a transcriptional repressor. In the breast cancer cell line MCF-7, exogenous ets-2 repressed the activity of a BRCA1 promoter-luciferase reporter dependent on a conserved ets-2-binding site in this promoter. Conditional overproduction of ets-2 in MCF-7 cells resulted in repression of endogenous BRCA1 mRNA expression. To address the mechanism by which ets-2 could act as a repressor, a biochemical approach was used to identify proteins that interacted with the ets-2 pointed domain. From this analysis, components of the mammalian SWI/ SNF chromatin remodeling complex were found to interact with ets-2. Brg-1, the ATP-hydrolyzing component of the SWI/SNF complex, along with the BAF57/p50 and Ini1 subunits could be co-immunoprecipitated from cells with ets-2. The pointed domain of ets-2 directly interacted in vitro with the C-terminal region of Brg-1 in a phosphorylation-dependent manner. The combination of Brg-1 and ets-2 could repress the BRCA1 promoter reporter in transfection assays. These results support a role for ets-2 as a repressor and indicate that components of the mammalian SNF/SWI complex are required as co-repressors.The ETS family, encompassing approximately 30 vertebrate members, encodes for sequence-specific DNA-binding proteins that are transcriptional activators and repressors (1). The family is defined by a highly conserved DNA binding domain referred to as the ETS domain. However, the DNA-binding properties of these factors are similar and cannot entirely account for the specificity required for the precise activation of target genes that occurs during the diverse biological processes mediated by individual family members. Modification of discrete family members by signal transduction pathways provides an additional mechanism to determine specificity (1).For example, members of the ETS family of transcription factors are important for mediating both transient and persistent changes in gene expression patterns in response to rassignaling pathways (2-4). The ETS family member elk-1 and related factors are directly phosphorylated by mitogen-activated protein kinases (MAPK), 1 a modification required for the activation of immediate early target genes like c-fos (2). Similarly, phosphorylation of the ETS family members ets-1 and ets-2 by ras-dependent pathways leads to persistent expression of target genes including extracellular proteases such as urokinase plasminogen activator (uPA) and stromelysin/MMP-3 (3, 4). Ets-1 and ets-2 are phosphorylated at a conserved residue (threonine 38 and threonine 72, respectively) by the well characterized ras-effector pathway, the Raf/MAPK pathway (4 -7). Additionally, the same residue in ets-2 can also be phosphorylated by another major ras-effector pathway, the phosphatidylinositol 3-kinase/Akt pathway (8).Understanding at the molecular level how phosphorylation modifies the activity of ets-1 and ets-2 will be cri...

Transcription Factor ets-2 Plays an Important Role in the Pathogenesis of Pulmonary Fibrosis

“…Interestingly, the association of BS69 and ets-2 is decreased when ets-2 is phosphorylated at the pointed domain, which contains the threonine-72 residue (31). Although several other co-repressors are thought to function coordinately with ets-2, including brahma-related gene 1 and the switch/sucrose nonfermentable (SWI/SNF) complexes (32), the mechanisms by which altered genetic co-repression contributes to the pathogenesis of pulmonary fibrosis require further study.…”

MTA1-mediated transcriptional repression of BRCA1 tumor suppressor gene

“…Although hyper-methylation and loss of heterozygosity on chromosome 17 has been associated with sporadic breast cancer, very little is known about BRCA1's transcriptional repression (Turner et al, 2007). Recent data suggest that the Ets-2 transcription factor may play a role in the repression of the BRCA1 promoter (Baker et al, 2003). The notion that MTA1 might be a corepressor was merely speculative until the recent discovery that MTA1 associates with histone deacetylases (HDACs) and thereby helps to repress estrogen receptor-a (ERa) transactivation in breast cancer cells (Mazumdar et al, 2001;Talukder et al, 2003).…”

SWI/SNF: The crossroads where extracellular signaling pathways meet chromatin

“…In addition to the transcriptional activator functions, we have herein described that SWI/SNF can repress transcription in concert with pRb and HDAC, and possibly with the SUV39H1/HP1 complex (Nielsen et al, 2001), as for cyclin E, cyclin A, and cdk1 genes during cell cycle regulation. Moreover, BAF57 interacts with MeCP2, the methyl-CpG binding protein mutated in Rett Syndrome (Harikrishnan et al, 2005), and the transcriptional repressor Ets-2 (Baker et al, 2003), evidencing that SWI/SNF is also involved in the maintenance of the inactive state of the chromatin.…”